Low hydrogen basic metal cored electrode

ABSTRACT

A consumable welding element for arc welding comprising a steel sheath surrounding a compacted core containing metal alloying powders and an essentially 100% basic compound in an amount less than about 1.60% of the total weight of said element. The basic compound is calcium fluoride powder which is preferably in the range of about 0.1% to about 0.9% calcium fluoride powder by total weight of the element. As another feature the core of the element contains a specific agent for decreasing the amount of diffusible hydrogen in the weld metal. This new element may be a filler metal for TIG welding; however, it is preferably a consumable electrode for MIG welding.

This application is a continuation-in-part of pending application Ser.No. 405,727, filed Sept. 11, 1989 U.S. Pat. No. 5003155.

The present invention relates to the art of consumable welding elementssuch as filler metal and electrodes of the consumable type employed inarc welding and more particularly to a basic, metal cored electrode.

BACKGROUND OF INVENTION

The present invention relates to a consumable welding element which canbe used as filler metal for TIG welding or as the consumable electrodein MIG welding; however, it has more applicability to MIG welding ofhigh strength metals of the type demanded in certain military andindustrial applications and it will be discussed with respect to thatapplication. This discussion is applicable to all uses of the invention.

In the art of electric arc welding it is common practice to use a MIGprocess wherein a metal wire is advanced toward the workpiece while anelectric arc is created between the wire, referred to as a consumableelectrode, and the workpiece for the purpose of melting the end of thewire or electrode to deposit metal onto the workpiece. Such MIG weldingprocess involved highly developed and sophisticated technology in thearea of the precise composition of the electrode which is consumed inthe welding process. The composition of the electrode, the fluxingsystem, the type of electrical current, the shielding gas and otherfactors are adjusted and manipulated to obtain the desired weldingobjectives. One primary objective of any arc welding process is toobtain a high deposition rate which for the MIG process is usuallyindicated as a rate exceeding about 5 lbs/hr for welding in the verticalplane. The resulting weld metal must have a good bead formation, lowamounts of slag formed over the weld bead, and other physicalcharacteristics, which decrease the amount of labor needed to clean theresulting welded joint after the welding process. In addition, the weldmetal, or bead, of the joint itself must have physical properties suchas low cracking tendencies and high impact strength, sometimes measuredas the Charpy impact value. In addition, it is desirable to be able toemploy the welding electrode in not only a down hand position, but alsowelding out-of-position. All of these objectives have been the subjectof substantial patented art. Details of electrode compositions need notbe repeated for a person skilled in the art to understand the presentinvention.

As the yield strength of the workpiece metal increases to high strengthlevels, such as military specs HY-80, HY-100 and, even HY-130, seriousproblems have been experienced in obtaining low cracking and high impactstrength while maintaining the ability to weld out of position at highdeposition rates. When welding these high yield strength steels such assteels exceeding HY-80 (80,000 psi), the consumable electrode hasheretofore normally taken the form of a solid metal wire with an out ofposition diameter generally about 0.045 inches and with the down handdiameter generally about 0.062 inches. Welding of high yield strengthsteels including and exceeding over HY-100 has been extremely difficulteven with such solid MIG wire.

The object of the present invention is to provide a consumable electrodefor MIG welding or filler wire for TIG welding, which can be used forhigh strength steels over HY-80 and ideally for steels with strength ashigh as HY-130. Efforts to accomplish this objective have, in the past,involved use of the solid wire with adjustments of the alloyingcomposition together with preheating the workpiece. These efforts havebeen less than successful. In the welding art, there is always atremendous impetus to improve the welding electrode for the purposes ofincreasing the ease at which high strength steel is welded with lowcracking and high impact results. This is the objective accomplished bythe present invention.

Attempts to use MIG welding for high yield strength steels (over 80,000psi) with high deposition rates and high quality welding have, asexplained, involved the use of solid wire. Such wire does have thecapabilities of creating a relatively low diffusible hydrogen level inthe weld metal; however, when a flux is required with the electrode, thediffusible hydrogen in the weld metal increases. This increases thetendency for the weld metal to crack upon solidification. In view of thetendency of fluxing compounds to increase the diffusible hydrogen in theweld metal, it has been generally perceived that metal cored electrodesfor the MIG process would not be satisfactory for high strengthapplications such as those previously mentioned. The processing andcomposition of the core materials also increased the amount of oxygen inthe weld metal. Thus, when extremely high yield strength is employed,such as in the hull of ships, the military specifications have generallyrequired the use of solid welding wire. This limited the out-of-positiondeposition rate to about 6 lbs/hr, which was obtainable only byelaborate electrical pulsing techniques. Irrespective of that, themilitary has not been satisfied with such solid welding wire forapplication above yield strengths of HY-100 steel. If flux coredelectrode were employed, diffusible hydrogen of a higher level wasexperienced in the weld metal which increased the tendency of cracking.The use of solid welding wire for welding high yield strength steelsbecame the normal and only acceptable practice. To increase themechanical properties of the weld joint, the base metal was often heatedprepapatory to welding. Such solid wire electrode material also wascompelled to contain the alloying materials in precise percentages.Consequently, accurate control over the alloying composition of thesolid wire was extremely critical. This is a difficult metallurgicaltask.

In the welding industry, cored electrodes are quite commonly employedfor MIG welding. Such cored electrode reduce the criticality of thealloying metal forming the tubular component of the electrode. This isaccomplished by incorporating the alloying metals within the core invery precise proportions to obtain the desired alloying characteristicsand percentages in the resulting weld metal. Although the use of a coredelectrode with a metal powder core for controlling the composition ofthe weld metal does enhance the ability to control the actualcomposition of the weld metal, a metal cored electrode has a tendency tointroduce a substantial amount of oxygen into the weld metal and cause adecrease in the impact strength of the weld metal. In addition, fluxingingredients are required when using metal cored electrode in criticalhigh strength applications. This results in higher diffusible hydrogenin the weld metal than was experienced in use of solid wire. Inaddition, such metal cored electrode material was somewhat sensitive todifferences in electrical stick-out during the welding process. Thisdisadvantage was attributed to moisture in the electrode core and seamand moisture in the shielding gas around the electrode. Thus, the use ofmetal cored electrodes with all of their advantages with respect tocontrolling the actual composition of the weld metal had seriousdeficiencies and were not employed for solving the problem of weldinghigh yield strength steel of the type experienced in the ship buildingindustry. In addition, cored electrodes were not generally employed inpulsed welding processes, such as employed in out of position welding ofhigh strength steels.

Through the years the technology associated with welding high yieldstrength steel (over 80,000 psi) has involved a sophisticated MIGwelding process using a solid welding wire. Suggestions to employ ametal cored electrode have met with a lack of acceptance. The use ofmetal powder alloys in the core of the electrode solved the criticalitydifficulties associated with precise percentages required in the weldmetal; however, use of such a cored electrode increased the difficultiesexperienced with hydrogen and oxygen in the weld metal of the resultingjoint. These disadvantages made use of metal cored electrode for highstrength steel inappropriate. In view of the disadvantages involved inuse of metal cored electrodes for MIG welding of high yield steel, it isnot surprising that the use of flux cored electrodes has been limitedfor high yield strength welding. Problems recognized for metal coredelectrodes were present in flux cored electrodes. However, flux coredelectrodes had still additional limitations.

A common flux cored electrode is one having a titanium dioxide fluxingsystem formed as powders in the core and surrounded by a low carbonsteel sheath. Such flux cored electrodes provide good welding at highdeposition rates, up to 8 lbs/hr, can be used out-of-position. However,such electrodes result in a higher level of diffusible hydrogen than canbe employed in even HY-80 steel. In addition, the oxygen produces arelatively low Charpy strength. Consequently, the use of mild steel fluxcored electrode employing the normal titanium dioxide fluxing systemproduces good welding characteristics, with high deposition rates andrelatively high acceptance by the operator; however, the resulting weldmetal has oxygen and hydrogen at a level which is not acceptable, formost high yield strength steels. Due to the extremely high quality andhigh deposition rates obtainable by other flux cored electrodes, it hasbeen suggested to use a basic flux cored electrode employing such basiccompounds as calcium fluoride. These electrodes do produce good impactstrength, since the fluorine has a tendency to scavenge the oxygen fromthe weld metal; however, such basic flux cored electrodes can not beused satisfactory for out of position welding. Basic flux coredelectrodes are not generally acceptable to the welder since their use isgenerally limited to down hand welding. Consequently, basic flux coredelectrodes have not been employed for this type high yield strengthwelding.

In summary, metal cored electrodes, flux cored electrodes and basic fluxcored electrodes have not heretofore been used acceptably in MIG weldingof high yield strength steels, i.e. steels greater than about 80,000 psi(HY-80). Only solid wire electrode has been widely accepted in themilitary and industry for this high yield strength mechanized weldingapplication.

INVENTION

The present invention relates to a welding element, such as an electrodeor filler wire, which element can be employed for welding high yieldstrength steels, exceeding HY-100. Indeed, the electrode is applicablefor HY-130 steel. This improved electrode is a basic, metal coredelectrode which does not have the disadvantages of basic flux coredelectrodes, as explained above, which disadvantages resulted inuniversal use of solid metal wire for the MIG welding process whenwelding high yield strength steels exceeding HY-80. The presentinvention relates to a basic, metal cored electrode which can be usedfor out of position welding, obtains a deposition rate substantiallygreater than 5.0 lbs/hr, requires a fewer number of passes and producesa resulting weld bead which essentially duplicates a solid wire weldbead, wherein only minor islands of slag form along the surface of thebead.

In accordance with the present invention there is provided a basic,metal cored electrode which can be employed for MIG welding of highyield strength steels exceeding 100,000 psi or a cored filler wire forthe same purpose. In accordance with the present invention there isprovided a consumable arc welding electrode or welding elementcomprising a steel sheath surrounding a compacted core containing metalalloying powder. This core also includes an essentially basic compoundin an amount less than about 1.6% of the total weight of the element,i.e. the electrode. The metal alloying powder employs standardtechnology to determine the alloying composition of the resulting weldbead. The basic compound provides a single ingredient fluxing agentwhile reducing the oxygen in the weld metal to a level less than about0.04% of the weld metal. In accordance with the invention, the 100%basic compound is calcium fluoride powder.

In accordance with another aspect of the present invention, the calciumfluoride powder is contained within the core at an amount between about0.1% to about 0.9% of the total weight of the electrode. By having thislow percentage of fluxing ingredients, namely calcium fluoride powder,the previously experienced welding problems with flux cored electrodesis overcome, while the calcium fluoride controls the amount of oxygen inthe resulting weld metal.

In accordance with still another aspect of the invention, the basic,metal cored electrode includes a small amount of an agent for reducingthe amount of diffusible hydrogen in the weld metal. This agent has amelting point less than about 1,000° F. so that it may be incorporatedin the core material in particulate form and retain its compositionduring forming and drawing of the electrode. This agent releasesfluorine for the purpose of capturing diffusible hydrogen in the weldmetal during the arc welding process. The polymer can be increased to0.4% of the electrode weight. This results in a diffusible hydrogen ofless than 1 ppm and as low as 0.6 ppm, a level of diffusible hydrogennever before obtainable. The hydrogen scavenging polymer can not beemployed in a solid metal wire electrode. The polymer would be consumedin any melting or alloying process for producing a solid wire.

In accordance with the primary aspect of the present invention, thebasic metal cored electrode includes, as the single ingredient fluxagent, calcium fluoride powder in the core in addition to the powderemployed for hydrogen scavenging, such as a polymer containing fluorine.Metal alloying powder is also incorporated in the core with the singlebasic ingredient and the hydrogen scavenging polymer. The core issurrounded by a low carbon sheath which can be drawn into an electrodeless than about 0.100 inches in diameter. Of course, it is conceivablethat the sheath of the electrode could be formed in an electric alloyingfurnace to avoid the necessity for alloying metal powder in the core ofa consumable electrode. However, an important feature of the presentinvention is the implementation of a basic metal cored electrodeemploying a single ingredient which is 100% basic and generally inert,together with a hydrogen scavenging agent. Whether the alloying metal isin an accurately controlled sheath metal or is controlled by metalalloying powder in the core, is not critical to this important feature.The alloying concepts technology and results can be modified inaccordance with normal skill of the art. However, a distinct advantageresults from employing the alloying metals in the core. Thus, theinvention involves a basic metal cored electrode which can replace asolid wire getting the same results, but with the advantage ofdecreasing the oxygen in the weld metal and reducing the amount ofdiffusible hydrogen. This is a new concept and has never been done inthe welding art. By this invention, MIG welding of extremely highstrength steels has been accomplished, even in out of position welding.

The basic, metal cored electrode of the invention is a developmentcontrary to the customary wisdom in the arc welding field for MIGwelding of high yield strength steel. Due to the limitation of coredelectrodes, the prior welding technology involved the use of solid metalwire which in turn had the disadvantages previously described. It wasnot satisfactory for steel with a yield strength over 80,000 psi. Theinvention involves the use of a 100% basic compound which is inert,within a core of an electrode. Calcium fluoride powder is employed forthis purpose. In the past, when using calcium fluoride powder in thecore of an electrode, the calcium fluoride is present in relatively highpercentages to balance the normal acidic flux constituents. Since thecalcium fluoride percentage was relatively high, out-of-position weldingwas difficult. Thus, the art did not teach the use of calcium fluorideas an ingredient in a successful cored electrode for use in high yieldstrength out-of-position welding applications. In accordance with theinvention, calcium fluoride powder is employed; however, it is used in anovel manner. The calcium fluoride is used in the invention as thesingle fluxing ingredient in the core of the electrode. There is nofluxing system, such as the normal TiO₂ system or a basic flux system.The term "system" means two or more fluxing ingredients which react tocreate the fluxing action. The novel concept of the invention is thecalcium fluoride coacting with no other fluxing agent, but performing asthe fluxing agent by itself. In accordance with the invention, theamount of calcium fluoride is reduced to a level below about 1.6% byweight of the total electrode and preferably below 0.9% by weight. Atthis low amount of calcium fluoride, the fluxing action is accomplishedby the calcium fluoride itself. There is no fluxing system. By reducingthe calcium fluoride powder to a level below 1.60% and preferably below0.9% of the electrode weight, the calcium fluoride controls the oxygenin the weld metal without producing the poor welding operation and theinability to weld out-of-position normally associated with a flux coredelectrode having a larger volume of calcium fluoride. The calciumfluoride can be reduced even below the aforementioned upper limit(1.60%) without affecting the welding operation; however, as the lowerlimit of calcium fluoride approaches 0.2%, the amount of oxygen in theweld metal increases to a level which reduces the impact strength of ahigh yield strength steel for which the electrode is especiallydeveloped. Since the calcium fluoride is 100% basic and inert, itproduces a single flux agent or ingredient for the cored electrode.Since the calcium fluoride is limited at its upper percentage to createthe improved electrode, the fluorine available from the calcium fluoridefor use in the weld metal is limited. Since fluorine is an agent forreducing the diffusible hydrogen, which causes cracking associated withmost efforts to weld high yield strength steel, the present invention,incorporates as an additional ingredient, a hydrogen reducing agent.This agent, is novel and decreases the amount of diffusible hydrogen inthe weld metal. The reducing agent is a polymer containing fluorinewhich can be in an amount up to 0.4% by weight. This allows reduction ofthe diffusible hydrogen to less than 1 ppm (1 ml/100 g).

As so far described, the invention employs calcium fluoride powder in arelatively low amount within a precise range, together with a smallamount of an appropriate hydrogen reducing agent, such as a polymercontaining fluorine.

In its practical implementation, the invention is a basic metal coredelectrode; therefore, alloying metals for the weld metal are in powderform and compressed in the core. Of course, it is conceivable that thealloying materials could be incorporated into the surrounding sheath ofthe electrode if metallurgical accuracy can be obtained in the alloyingof the sheath steel. In accordance with the preferred embodiment of theinvention and in the most practical embodiment of the invention, a lowcarbon or low alloy steel sheath is employed for surrounding the core.The alloying metals are incorporated as powder in the core.Consequently, the invention is referred to as a basic, metal coredelectrode. The electrode is drawn into the desired size which,preferably, is a cylinder less than 0.100 inches in diameter. Thisdrawn, cored wire, constructed in accordance with the present invention,is used for MIG welding to obtain all of the advantages of a coredelectrode together with the advantages of a solid wire electrode. Byusing a single basic constituent in low quantities, within the coretogether with a novel hydrogen reducing agent, oxygen and hydrogen inthe weld metal are reduced. The welding electrode can be employed forwelding high yield strength steel, such as steel with minimum yieldstrength of 100,000 psi (HY-100) and, even 130,000 psi (HY-130) Inaccordance with the invention, this basic metal cored electrode can beused to weld out-of-position since the calcium fluoride is at acontrolled, limited maximum: level, which is less than 1.60%, and thiscalcium fluoride constitutes the only fluxing constituent within or onthe electrode.

By employing the present invention, calcium fluoride is the singlefluxing ingredient within the core and the resulting electrode weldsessentially in the same fashion as solid MIG wire, such asout-of-position welding and/or pulse welding. The advantages of a coredelectrode are retained with the advantages of a solid wire electrode.

In the past, the use of a metal cored electrode produced higher levelsof oxygen. This oxygen, in the invention, is reduced by inclusion ofcalcium fluoride particles or powder in the core; however, the level ofinclusion of calcium fluoride is restricted to small amounts less than1.60% so that the difficulties previously experienced in using calciumfluoride, i.e. inability to pulse weld out-of-position, is not adetrimental characteristic of the present invention. Reduction of thecalcium fluoride in the core as used in the present invention is novel.One aspect of the invention was based upon the recognition that higherlevels of calcium fluoride as used in a basic flux system were notrequired, if the flux was only calcium fluoride. In this manner, a basicflux is created by the calcium fluoride. By removing the otherconstituent of the basic flux system, calcium fluoride can be used insmaller amounts. By reducing the amount of calcium fluoride, the weldingcharacteristics of the electrode are made acceptable. Thus, theinvention involves controlling the chemistry of the calcium fluoride toemploy only enough calcium fluoride to scavenge the oxygen in the weldmetal. The calcium fluoride is not one of several constituents in abasic flux system. The calcium fluoride of the invention forms the totalbasic flux constituent. By such control of the calcium fluoridechemistry, a basic metal cored electrode is produced which has betterwelding characteristics than a solid wire electrode. The calciumfluoride is of sufficient amount to control the oxygen in the weld metalto minimize any decrease it would otherwise cause in the impact strengthof the resulting weld. Of course, alloy metals in the core or in themetal of the sheath surrounding the core can be incorporated foraffecting the Charpy notch strength, without departing from the thepresent invention.

Since additional amounts of calcium fluoride in the electrode are notneeded to offset other fluxing constituents of a total multiplecomponent flux system, the electrode is useful in pulse weldingout-of-position to the same extent as a solid MIG wire electrode. Thus,a basic cored electrode is provided with a single fluxing ingredientwhich is 100% basic and inert. Such single ingredient fluxing isdistinguished from other fluxing systems of the type including titaniumdioxide which is detrimental to the notch toughness of the weld metal.Use of a conventionally fluxed electrode is not applicable for weldinghigh yield strength steel of the type now employed by the military withsteel that approaches HY-100 or greater.

In the past, there have been metal cored electrodes and basic flux coredelectrodes. These two electrodes were never considered as replacementsfor solid wire when employing MIG welding of high yield strength steel,such as used in naval vessels, military and commercial. Basic flux coredelectrodes, as previously mentioned, are not applicable forout-of-position welding. They have lower operator appeal and lowdeposition rates, less than 5.0 lbs/hr. The present invention relates toa cored electrode which is a combination of metal and basic which isapplicable for the purposes described in this application. Thenon-metallic ingredients in the core are limited to calcium fluoride andthe polymer containing fluorine hydrogen removing agent, if selected.There are no other non-metallic materials forming a total fluxing systemas is normal in the industry.

It has been found that a basic, metal cored electrode, as so fardescribed and constructed in accordance with the present invention, ishighly advantageous for welding high yield strength steel and can besubstituted for solid wire electrode material. However, to produce asuperior cored electrode, the present invention also envisions aconstituent for reducing the diffusible hydrogen of the weld metal. Suchhydrogen is believed to be derived from moisture entering the seam ofthe sheath surrounding the core by capillary action or otherwise.Tendency for cracking increases with increases in the yield strength ofthe base metal being welded. Thus, as the strength increases, the amountof hydrogen which can be tolerated in the weld metal decreases. Hydrogenenters the weld metal from contaminants within the core, from lubricantsplaced on the electrode and from drawing compounds used in processingthe electrode and from other sources. The military specificationsrequire less than 2 ml/100 g for welding at room temperature for steelwithin the range of 82,000-88,000 psi. To attempt to accomplish thiswith the solid wire, the wire is cleaned after processing. This cleaningreduces the ability to feed the wire and still meet these requirements.Heating of the base metals has a tendency to drive moisture from thebase metal surface. Thus, heating before welding is another way oflimiting hydrogen in the weld metal. To reduce hydrogen, some companiesmake seamless tubes for the cored electrodes to limit moisture enteringthrough the seam of the tube into the core material. However, no matterwhat procedures are used, hydrogen is still present in the weld metal.The hydrogen originates from the moisture in the shielding gas and fromhydrogen on the surface or entrapped in the joint between the base metalstructures being welded. Other sources of hydrogen exist to complicateany physical procedure for elimination of the small amounts which cancause problems in high strength steels, i.e. greater than about 80,000psi. Thus, the present invention is directed toward a concept ofaccepting the existence of unwanted, minute quantities of hydrogen andremoving the minute quantities by a novel formulation of the electrode.Since the amount of calcium fluoride is relatively low, only a smallamount of fluorine is available to reduce the diffusible hydrogen.However, the level of hydrogen must be below 2 ppm for high yieldstrength steel, such as HY-100, especially when welded at roomtemperature. The present invention can reach this goal by using calciumfluoride in the limited amount. However, it is quite desirable to reducethe hydrogen even below the 2 ppm limit recognized by militaryspecifications as a requirement for high yield strength welding. Inaccordance with the invention, a hydrogen reducing agent is employed toreduce the detrimental diffusible hydrogen. This agent is a polymercontaining fluorine such as a fluocarbon. This agent evolves fluorine tocombine with the diffusible hydrogen. It is solid at the temperaturesused in processing electrodes. This can be accomplished by using apolymer capable of withstanding a temperature of about 1,000° F. Theagent of the polymer type must be able to be particulated into finepowder for the purposes of mixing with metal powder and calcium fluoridepowder. The polymer type agent must be deliquiescent, andnon-hygroscopic and otherwise inert. Of course, there could be nohydrogen atoms nor any nitrogen atoms in the polymer. In the preferredembodiment the polymer type agent described above, is employed withcalcium fluoride powder to produce the system that is combined with themetal alloying powders in the core of the electrode. The fluorine fromthe small amount of calcium fluoride assists in removing hydrogen. Thepolymer containing fluorine reduces the amount of hydrogen even furtherand results in substantially less than 2 ppm of hydrogen in the weldmetal. As is known, hydrogen in the monatomic state is a primarydeleterious constituent causing cracking in the weld metal. Combining ofhydrogen with fluorine reduces this type of free hydrogen. In addition,if hydrogen combines with itself to form a hydrogen molecule, it doesnot affect seriously the cracking characteristics of the weld metal.Thus, fluorine reduces the cracking tendency of the weld metal. Thissubstantial decrease of the diffusible hydrogen is even more beneficialwhen notch toughness is a problem such as in HY-130 steel.

As discussed previously, cored electrodes in the past have beensensitive to stick out variations with respect to the amount of hydrogenwhich is found in the weld metal. It has been determined that thehydrogen reducing agent contemplated by the present invention does nothave substantial stick out sensitivity and produce essentially the samelevels of diffusible hydrogen in the weld metal for normal variations instick out in a MIG welding process.

In accordance with the invention, a low carbon steel sheath surrounds acore of particulate material which is reduced in diameter to compact thecore material with an outer diameter of less than 0.100 inches. Suchmild or low alloy steel sheath surrounds a small amount of calciumfluoride powder and a trace of the hydrogen reducing polymer containingfluorine. Metal powder is included in the core for the purpose ofalloying the resulting weld metal deposited by use of an electrodeconstructed in accordance with the present invention. By thisconstruction, there is produced a basic metal cored electrode which canreplace a standard solid wire for use in MIG welding of high yieldstrength steel and the resulting diffusible hydrogen is less than 2 ppmand, with 0.02-0.04 percent of the polymer, less than 1 ppm. This hasnever been done before. The invention can be used for filler wire to TIGwelding also.

The primary object of the present invention is to provide a somewhatconventional metal cored electrode with a basic ingredient, such aspowdered calcium fluoride. This produces a family of basic metal coredelectrodes.

Another object of the present invention is the provision of a basic,metal cored electrode which can be used in a situation wherein lowerweld metal oxygen content is demanded. The oxygen content is controlledby the chemistry of the basic ingredient, such as powdered calciumfluoride.

A further object of the present invention is the provision of a coredelectrode that can be used in pulse welding out-of-position in a mannerheretofore reserved in MIG welding for solid wire electrodes.

Another object of the present invention is the provision of a coredelectrode with agents in the core to reduce the diffusible hydrogen inthe weld metal.

Still a further object of the present invention is the provision of abasic, metal cored electrode that can be used in high yield strengthsteel welding applications such as HY-80, HY-100 and HY-130 wherehydrogen cracking is more prevalent.

In accordance with still a further object of the present invention isthe provision of a cored electrode providing calcium fluoride in thecore at a level in the general range of 0.1% to 1.6% by weight of theelectrode and preferably in the range of 0.1% to 0.9%. Since thefluorine within the welding arc creates a pinching effect which producesspattering and slag ingredients in the metal cored electrode alsodeteriorates welding speed in out-of-position pulse weldingapplications, the limitation of calcium fluoride in an electrode to nomore than about 0.9% of the total electrode weight increases the qualityof the resulting weld using the present invention.

Yet another object of the present invention is the provision of a coredelectrode for use in high yield strength welding wherein a lower oxygencontent produces higher impact properties and improves the weld metalmicrostructures.

Another object of the present invention is the provision of a basic,metal cored electrode for use in high yield strength welding which mayemploy calcium fluoride or barium fluoride powders or possibly lithiumfluoride, sodium fluoride or potassium fluoride powders. In accordancewith the preferred embodiment of the invention, calcium fluoride powdersare employed.

These and other objects and advantages will become apparent from thefollowing description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a schematic cross sectional view of a basic metal cored electrodeconstructed in accordance with the present invention;

FIG. 2 is a cross sectional view of a modification of the preferredembodiment of the present invention;

FIG. 3 is a graph illustrating the relationship between the basiccomposition of the electrode and the weld metal oxygen content; and,

FIG. 4 is a graph showing the relationship between the percentage of apolymer containing fluorine of the total electrode weight and theconcentration of diffusible hydrogen in the weld metal.

PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for the purposeof illustrating a single example of the present invention. In thisexample, two plates one inch thick are welded with a shielding gasincluding 98% argon and 2% oxygen with a heat input of 55-110kilojoules/inch with a preheat of the plates to a temperature of 250° F.The plates are formed from a high yield strength military steel HY-100.A basic metal cored electrode 10 was provided with an outer low carbonsheath 12 joined together at a seam 14, as schematically illustrated inFIG. 1. This figure shows features of the invention which will bedescribed generally.

The seam 14 of sheath 12 may be overlapping or otherwise formed inaccordance with standard practice for making welding rod 10. Withinsheath 12 is a core compacted together and formed from particles 20 ofalloying material (shown as squares), calcium fluoride particles 22(shown as large circles) and a small amount of polymer containingfluorine particles 24 (shown as small circles). This core is compactedby drawing electrode 10 to a diameter less than 0.100 inches. In thisexample, the polymer containing fluorine is 0.16% of the total electrodeweight for Example A or 0.40% by weight for Example B. (see FIG. 4). Thepercentage of total electrode weight for the calcium fluoride particlesis 0.5%. The metal alloy particles 20 have a percentage of about 19% ofthe total weight of the electrode. The remaining weight is the sheath ortube 12. Examples A and B produce a satisfactory weld for high yieldstrength military steel such as HY-100.

FIG. 2 is a modification of the preferred embodiment of the inventionwherein the core within sheath 12 includes only the calcium fluoridepowder 22 and the hydrogen reducing agent powders 24. In this instance,the metal forming sheath 12 includes the alloying agents. The variouscompositions of alloying agents is not a part of the present inventionand may be adjusted without departing from the present invention whichrelates only to the concept of an essentially single fluxing ingredient,i.e. calcium fluoride, together with alloying powder in the core with,in the preferred aspect, the addition of a hydrogen reducing agent inthe core. As can be seen, this invention is not directed toward conceptsand technology related into the selection of the alloying agent for theparticular welding operation being performed.

Referring now to FIG. 3, the calcium fluoride particles within the coreare less than about 1.6% of the total weight of the electrode. At 1%, orat a position near that amount calcium fluoride, the welding qualitystarts reducing its acceptability and a value over about 1.6% wouldresult in a welding electrode not satisfactory for use in welding highyield strength steels in various welding positions. As the calciumfluoride decreases, the amount of oxygen in the weld deposit increases.As the yield strength of the high yield strength steel increases, alesser amount of oxygen can be contained in the weld metal to meetmilitary specifications and give acceptable impact strength. For highyield strength steel in the higher range, such as HY-130, the amount ofincluded weld metal oxygen must be less than for high strength steelsuch as HY-80. Thus, the minimum level of calcium fluoride for HY-130 isat position A on the graph. For high strength steel with a lowerstrength, such as HY-80, the oxygen included in the weld metal can beslightly higher. This concept is illustrated at position B on the graph.Thus, the minimum limit of calcium fluoride varies according to theyield strength of the high yield strength steel to which the inventionis specifically applicable. In all instances, the weld metal alloy has alow oxygen content which is required for welding high yield strengthsteel. The ability to include more oxygen is only illustrated in FIG. 3for the purpose of describing the invention and showing the minimumlimits for the calcium fluoride needed in practicing the presentinvention.

Referring now to FIG. 4, in this graph, the percentage of polymercontaining fluorine, such as tetrafluoroethylene, is compared to thediffusible hydrogen found in the weld metal. The value for hydrogen isindicated by the parameter ml/100 g which has a generally directrelationship with ppm. In practice, the high yield strength steelsshould have diffusible hydrogen less than 2.0 ppm. Hydrogen of less than1.0 ppm has been generally unattainable except under extreme controlledconditions not applicable for use in the field. As can be seen, byincorporating calcium fluoride powder with the metal alloying powders,this objective of less than 2.0 ppm is reached, even without anyhydrogen reducing agent. However, in accordance with an aspect of theinvention, a hydrogen reducing agent is incorporated to reduce evenfurther the hydrogen in the weld metal. By including 0.16% of polymercontaining fluorine as used in the first example A, a small amount ofthe hydrogen reducing agent drastically reduces the hydrogen of the weldmetal. Thus, the preferred embodiment of the invention, and one aspectof the invention, involves the use of such a hydrogen reducing agent todecrease the amount of detrimental diffusible hydrogen within the weldmetal. The upper solid line graph in FIG. 4 represents an electricalstick out for 3/8 inch. The lower solid graph is for an electrical stickout of 3/4 inch. As can be seen, the use of this agent to the core ofelectrode 10 has very small stick out sensitivity as it relates tohydrogen. This is an advantage over other arrangements for minimizingdiffusible hydrogen at these low levels. These two graphs are shownextended to Example A; however, they would extend to the ultra-lowhydrogen Example B at 0.4% polymer. To show how the reduction of sulfurto less than 0.008 percent of electrode weight and as low as 0.004percent of electrode weight can allow reduction of magnesium from about0.16 percent to less than 0.3 percent and, thus, increased polymer, theExample B is indicated. Example B is an actual example where the sulfurwas about 0.004 percent and the magnesium was less than 0.3. The weldmetal had diffusible hydrogen of about 0.6 ppm. This is a levelexcellent for welding high strength steel and not heretofore obtainablefor use in the field.

Having thus described the invention, the following is claimed:
 1. Aconsumable welding element for arc welding comprising a steel sheathsurrounding a compacted core containing an essentially single ingredientflux system formed from powdered calcium fluoride to provide fluxing forsaid welding element and making up less than 1.60% by total weight ofsaid element, said core having up to about 0.4% of an agent for reducingthe amount of diffusible hydrogen in the weld metal, said agentcomprising a polymer containing fluorine.
 2. A welding element asdefined in claim 1 wherein said core contains between about 0.1% andabout 0.9% calcium fluoride by total weight of said element.
 3. Awelding element as defined in claim 1 wherein said core contains lessthan about 0.30% of said hydrogen reducing agent by total weight of saidelement.
 4. A welding element as defined in claim 3 wherein said coreincludes powdered metal alloying materials.
 5. A welding element asdefined in claim 1 wherein said core contains in the range of 0.2% toabout 0.40% of said hydrogen reducing agent by total weight of saidelement.
 6. A welding element as defined in claim 5 wherein said coreincludes powdered metal alloying materials.
 7. A welding element asdefined in claim 1 wherein said core includes powdered metal alloyingmaterials.
 8. A welding element as defined in claim 7 wherein saidalloying materials and said steel sheath, taken together, contain carbonof less than about 0.2% of the total element weight.